The coherent light generated by edge emitting laser diodes is emitted in one or more planes that are substantially parallel to the boundaries between the semiconductor layers that form the laser. More recently, vertical cavity surface emitting lasers (VCSEL) have been developed. Unlike edge emitting laser diodes, VCSELs are laser diodes that are fabricated to emit light in one or more planes that are substantially perpendicular to the boundaries formed between their semiconductor layers. VCSELs appear to be advantageous over edge emitting laser diodes in several respects. For example, VCSELs generally require lower power and are less expensive to manufacture than their edge emitting counterparts.
An example prior art optical device 10 is shown in FIG. 1. In the example of FIG. 1, a VCSEL 12 is optically coupled to a photodetector 14 via a waveguide 16. Because, by definition, the light generated by a VCSEL is transmitted in a plane that is generally perpendicular to the surface of the VCSEL, the light from a VCSEL 12 is typically coupled to a waveguide 16 by an expensive and complicated end finish of the waveguide 16. For example, an end of the waveguide 16 may be cut and polished to form a 45 degree total reflection mirror 18 that re-directs a substantial portion of the light emitted by the laser 12 approximately 90 degrees from its initial path into the waveguide 16. Typically, the opposite end of the waveguide 16 is also formed into a 45 degree mirror 18 to re-direct the light from the waveguide 16 toward the photodetector 14 as shown in FIG. 1.
This complicated mechanism for directing the light generated by the VCSEL 12 to the photodetector 14 is expensive and difficult to manufacture. For example, to manufacture a device 10 such as that shown in FIG. 1, the die-substrate standoff height (e.g., the distance between the VCSEL 12 and a substrate 20 of the optical device 10 and/or the distance between the photodetector 14 and the substrate 20 (e.g., a printed circuit board) of the optical device 10) must be carefully controlled. Further, the optically active area of the VCSEL 12 must be precisely aligned with one of the end mirrors 18 of the waveguide 16 and the active area of the photodetector 14 must be precisely aligned with the opposite end mirror 18 of the waveguide 16.
The tolerances associated with the die-substrate height standoff requirements and the VCSEL-to-waveguide and waveguide-to-photodector alignment requirements dictate that the placement/bonding of the VCSEL 12, the photodetector 14, and sometimes the waveguide 16 be carried out through an active alignment technique. An active alignment technique is a feedback technique in which a laser (e.g., the VCSEL) associated with the component(s) being placed is energized, and the position(s) of the component(s) being placed are adjusted to maximize an output of the energized laser at an output of those component(s). When the output is maximized, the component(s) are aligned and bonded in place. Unfortunately, active alignment processes such as that described above are slow and do not lend themselves to mass production.
Additionally, prior art optical devices 10 such as that shown in FIG. 1 typically do not permit the use of two dimensional waveguide arrays. As a result, such prior art devices have limited bandwidth.